It’s not that people are unpredictable. They are predictable. But they frequently behave counterintuitively, a phenomenon that has given rise to the field of behavioral economics. Like economists, engineers have traditionally ignored psychology. Traffic: Why We Drive the Way We Do (and What It Says About Us), is a 300-odd page romp into what scientists are learning about how traffic really works now that they are accounting for the human element. Take “passive safety.” It’s long been the philosophy behind efforts to make driving safer. Reduce driver demands by simplifying the driving environment, and protect people from getting hurt in crashes—rather than teaching skillful driving. After all, it’s easier to engineer safety than change behavior. But too much safety lulls the driver into complacency.
Driving down Orlando’s US Highway 50 with author Tom Vanderbilt, Dan Burden, a traffic eminence, notes that trees have been eliminated, and the sidewalk pushed so far back from the street as to be in “another world,” all to relieve drivers of hazards and distractions. Nonetheless, this stretch is the 12th deadliest road in America.
Yet, nearby on 50, where lanes and clear zones are narrower, and dangerous “fixed objects”–poles and trees–remain, but where traffic is otherwise completely comparable, a fatality hasn’t occurred in five years. “The hazards [are] the safety device,” Vanderbilt writes. “Drivers left with little room for error seemed quite capable of not making errors.”
That concept extends to rotaries, which not only move traffic considerably more quickly than standard stoplight intersections, but are safer, even though–or rather because–drivers have to compensate for uncertainty by driving more carefully. This is the rationale behind the famous Dutch traffic engineer Hans Monderman’s counterintuitively safe blending of the worlds of pedestrians, cyclists, and motorists on narrow streets.
Oddly, Vanderbilt ignores this logic for highway speeds, an issue that has arisen as politicians use safety as an additional excuse to promote a new double nickel to address skyrocketing oil prices and climate change. Vanderbilt marshals considerable evidence to argue that slower is always safer, but he doesn’t dig into special cases.
Boosting the speed limit on Indiana interstates from 65-70 mph, which raised average speeds by more than 3 mph, did not lead to more injuries or deaths, according to a recent study. Investigator Fred Mannering of Purdue University largely credits reduced speed variance, and adds that greater alertness may also have played a role.
The take-the-human-out-of-the-equation approach combined with labor saving devices–slushboxes, radar cruise control, etc–leads yuppies to think they can multitask safely behind the wheel. Vanderbilt cites various studies to explain why they won’t get away with it. Attention capacity is limited, and easily breached. One of several examples: “pedestrians using mobile devices walked more slowly and were less able to interact with the device, pausing occasionally to “sample the environment”,” Vanderbilt writes. And stuff happens so quickly in traffic that more than two seconds’ inattention boosts the risk of collision 19-fold.
There’s much more. Vanderbilt dissects the frustrations of getting stuck in slow traffic. Anxiety, uncertainty, and boredom all slow time, as does the sense–oft illusory–that other lanes are moving quicker. He reports that driving is safest in the least corrupt countries. And he explains why adding more highways or lanes has diminishing returns, and why traffic increases to fill new capacity, through “latent demand.”
When a strike removed 9,000 trucks from the roads near Los Angeles, within a few days the traffic was as bad as ever. (Nonetheless, more than several years after completion of the Big Dig, it still takes me only 25-30 minutes–reliably–to drive to Boston’s Logan Airport, as compared to 45 minutes to an hour in the old days.)
There is no easy way to ease traffic, short of moving to the Great Plains or the Great Basin. But understanding its flows may make it slightly less intolerable.